Names That Mean Immortality

Tansy is a flower name rarer than Rose, livelier than Lily and a lot less teasable than Pansy. 
 Tansy is a perennial herbaceous plant of the aster family that has clusters of small bright yellow blossoms. It was cultivated by the ancients for medicinal purposes, and has found a variety of other uses over the ages, associated with health and immortality.
 There have been a couple of eponymous novels titled Tansy, and it was the name of a character on Hart of Dixie,

Tansy

Thanos originated as a short form of Athanasios, a Greek name meaning "immortal." It is composed of the elements a, a negative Greek prefix, and thanatos, meaning "death." St. Athanasius, who used the Latin spelling of the name, was a bishop of Alexandria and known for his opposition to Arianism.
 
Though this is a perfectly respectable Greek choice, be aware that Thanos the Mad Titan is a sinister Marvel Comics villain.

Names That Mean Immortality

The names

Tansy

Thanos